Sharif Digital Repository

One of the most important parts of oil industry is drilling with rotating drillstrings. In a drillstring because of the contact between bit and formation, contact between drillstring and borehole wall, existence of drilling mud, misalignment in drillstring and stick-slip phenomenon; axial, lateral and torsional vibrations is created. These vibrations may lead to fatigue failures and abrasive wear of tubular, damaging the drill bit and borehole wall. In this thesis the drillsting vibrations is studied using finite element method. To this end, cylindrical superslement with C1 continuity is presented. By using the shape functions of this superelement; kinetic and potential energy of drillstring... 

Cylinders are one of the most applicable components in industry. According to the application of these elements, reinforcement and stiffening are the common ways to enhance mechanical properties of them. Nowadays, by advent of new materials such as functionally graded materials (FGMs), a novel method of improving these structures is discovered. By application of FGMs, many physical and mechanical characteristics of these structures can be modified. In this thesis, vibration analysis and frequency optimization of a stiffened cylinder made from FGMs are performed. FGM which is employed in this investigation is made from two different materials, to have better modal properties which cause in... 

Angular contact bearings are utilized in many industrial types of machinery, including machine tools’ spindle. Spindle is one of the most important parts of a machine tool, which has a substantial impact on dynamic properties and stability of machining processes. Spindles’ motion takes place under guidance of bearings, which are mainly angular contact type. Since bearings’ loading under forces that are resulted from angular velocity and temperature increment are intensified, it is required to control the applied forces in operating situation, in order to predict the hardness, accuracy, efficiency, and life time of spindle. Thus, determining the dynamic performance of machine tool’s spindle,...